Vehicle detection using a magnetic field sensor

The measurement of vehicle magnetic moments and the results from use of a fluxgate magnetic sensor to actuate a lighting system from the magnetic fields of passing vehicles is reported. A typical U.S. automobile has a magnetic moment of about 200 A-m²(Ampere-meters²), while for a school bus it is about 2000 A-m². When the vehicle is modeled as an ideal magnetic dipole with a moment of 200 A-m², the predicted results from an analysis of the sensor-vehicle geometry agree closely with observations of the system response to automobiles.